Restatement and Revision of Previously Issued Unaudited Financial Statements - Effect of Revisions on Affected Line Items on Condensed Consolidated Balance Sheet (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Feb. 28, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Condensed Consolidated Balance Sheet Data:
Cash and cash equivalents	$ 206,638		$ 243,465	$ 171,970	$ 223,849
Restricted cash	6,693		3,478	7,629
Accounts receivable, net	106,308		78,928	55,475
Total current assets	417,411		386,580	380,278
Deferred income taxes	45,024		57,471	34,563
Total assets	783,286	6,614	675,204	662,850
Other current liabilities	52,185	3,060	106,796	60,641
Total current liabilities	355,307		327,023	331,775
Other liabilities	45,634		82,416	64,574
Total liabilities	674,601	46,114	549,439	571,349
Capital surplus	194,629		197,113	186,262
Retained earnings	950,202		967,473	891,875
Total shareholders' equity	108,685		125,765	91,501	169,105
Total liabilities and shareholders' equity	783,286		675,204	662,850
As Previously Reported [Member]
Condensed Consolidated Balance Sheet Data:
Cash and cash equivalents	210,012		246,342	178,476
Restricted cash	719		601	1,123
Accounts receivable, net	104,077		77,313	54,411
Total current assets	362,972		384,965	379,214
Deferred income taxes	56,858		56,112	34,081
Total assets	642,986		672,230	661,304
Other current liabilities	34,807		86,722	50,920
Total current liabilities	234,573		306,949	322,054
Other liabilities	100,138		98,327	72,629
Total liabilities	484,711		545,276	569,683
Capital surplus	204,219		206,703	194,027
Retained earnings	990,202		959,072	884,230
Total shareholders' equity	158,275		126,954	91,621
Total liabilities and shareholders' equity	642,986		672,230	661,304
Revisions [Member]
Condensed Consolidated Balance Sheet Data:
Cash and cash equivalents			(2,877)	(6,506)
Restricted cash			2,877	6,506
Accounts receivable, net			1,615	1,064
Total current assets			1,615	1,064
Deferred income taxes			1,359	482
Total assets			2,974	1,546
Other current liabilities			20,074	9,721
Total current liabilities			20,074	9,721
Other liabilities			(15,911)	(8,055)
Total liabilities			4,163	1,666
Capital surplus			(9,590)	(7,765)
Retained earnings			8,401	7,645
Total shareholders' equity			(1,189)	(120)
Total liabilities and shareholders' equity			2,974	1,546
As Revised [Member]
Condensed Consolidated Balance Sheet Data:
Cash and cash equivalents			243,465	171,970
Restricted cash			3,478	7,629
Accounts receivable, net			78,928	55,475
Total current assets			386,580	380,278
Deferred income taxes			57,471	34,563
Total assets			675,204	662,850
Other current liabilities			106,796	60,641
Total current liabilities			327,023	331,775
Other liabilities			82,416	64,574
Total liabilities			549,439	571,349
Capital surplus			197,113	186,262
Retained earnings			967,473	891,875
Total shareholders' equity			125,765	91,501
Total liabilities and shareholders' equity			$ 675,204	$ 662,850